Genetics - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: Gregor Mendel crossed a tall pea plant with a dwarf pea plant. F1 were all tall. F2 had both tall and dwarf.

Identify the dominant and recessive traits.
- Answer: Dominant: Tall (T). Recessive: Dwarf (t).
Why did the dwarf trait disappear in F1 and reappear in F2?
- Answer: It was masked by the dominant 'T' allele in F1 (Tt). It reappeared in F2 when two recessive alleles came together (tt).
Designing: F2 Punnett square and ratios.
- Answer: (T, t) x (T, t) -> TT, Tt, Tt, tt. Phenotypic Ratio: 3 Tall : 1 Dwarf. Genotypic Ratio: 1 TT : 2 Tt : 1 tt.
If Mendel chose Snapdragon (Incomplete dominance)?
- Answer: F1 would have an intermediate phenotype (e.g., Pink if parents were Red and White).
Why choose the pea plant?
- Answer: Short life cycle, many contrasting traits, easy to cross-pollinate, produces many offspring.

Case Study 2: Husband is color-blind, Wife has normal vision (father was color-blind). 6. Is color blindness autosomal or sex-linked?

Answer: Sex-linked (X-linked) recessive.

Genotype of the wife.
- Answer: $X^C X^c$ (Carrier). Since her father was color-blind ( $X^c Y$ ), he must have passed the $X^c$ to her.
Creating: Pedigree chart.
- Answer: [Description: Circle-Square connecting. Husband shaded, Wife half-shaded/dot].
Analysis: % chance son will be color-blind.
- Answer: 50%. The son receives Y from father and either $X^C$ (Normal) or $X^c$ (Color-blind) from mother.
Why more common in males?
- Answer: Males have only one X chromosome. A single recessive allele on the X chromosome is enough to cause the condition.

Section B: Assertion-Reasoning Questions

Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.

Assertion (A): A heterozygous individual expresses the dominant trait. Reason (R): The dominant allele masks the expression of the recessive allele.
- Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): The Law of Independent Assortment holds true for all pairs of characters. Reason (R): Linked genes do not assort independently.
- Answer: (d) A is false but R is true. (Linked genes are an exception).
Assertion (A): Haemophilia is known as "Bleeder's disease". Reason (R): It is an X-linked recessive disorder where blood fails to clot.
- Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Mutation is a sudden change in genes. Reason (R): Changes in gene structure can lead to variations.
- Answer: (b) Both A and R are true but R doesn't explain the "sudden" nature.
Assertion (A): In humans, the father determines the sex of the child. Reason (R): The egg contains X, sperm can carry X or Y.
- Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

Designing: Dihybrid cross RRYY x rryy.
- Answer: Gametes: RY and ry. F1: RrYy (Round-Yellow).
Creating: Genetic Profile Bbtt.
- Answer: Genotype: Bb (Heterozygous), tt (Homozygous recessive). Phenotype: Brown eyes (Dominant B), Straight hair (Recessive t).
Analysis: 25 short, 75 tall. Can you tell TT from Tt?
- Answer: No. Both TT and Tt look identical (Tall) due to dominance.
Designing: Law of Segregation flowchart.
- Answer: Parent (Tt) -> Meiosis -> Gamete 1 (T) and Gamete 2 (t) separate.
Visualisation: Locus and Alleles.
- Answer: [Diagram: Two bars. Same spot marked A on one and a on the other].
Application: Blood Group AB.
- Answer: Co-dominance. Both $I^A$ and $I^B$ alleles are expressed equally.
Creating: Two sparkling cats have a non-sparkling kitten.
- Answer: Parents must be heterozygous (Ss). Cross: Ss x Ss -> 25% ss (non-sparkling).
Analysis: "Criss-cross inheritance".
- Answer: Father passes the trait to daughter (carrier), who passes it to her son.
Designing: Pedigree checklist.
- Answer: 1. Do unaffected parents have an affected child? (Recessive). 2. Does every affected child have an affected parent? (Dominant).
Creating: Dialogue.
- Answer: Dominant: "I'm in charge here!" Recessive: "Fine, I'll wait until I meet someone just like me."

Section D: Competency & Critical Thinking

Genotype vs Genome.
- Answer: Genotype: Genetic makeup of an individual for a specific trait. Genome: Total genetic material (all genes) of an organism.
Scenario: Test Cross.
- Answer: Cross with 'tt'. If all offspring tall -> Parent is TT. If 50% tall, 50% dwarf -> Parent is Tt.
Critical Thinking: Two blue-eyed parents have a brown-eyed child?
- Answer: Impossible if blue is recessive and brown is dominant.
Application: Sickle Cell Anemia.
- Answer: Point mutation -> Valine instead of Glutamic acid -> Hb molecules clump -> RBCs become sickle-shaped.
Monogenic vs Polygenic.
- Answer: Monogenic: Controlled by one gene (e.g., Pea height). Polygenic: Controlled by multiple genes (e.g., Human skin color).
Diagram Based: Punnett square fill-in.
- Answer: (Standard 2x2 grid results).
Importance of Variation.
- Answer: Helps species adapt to changing environments, reducing extinction risk.
Analysis: Why X-linked recessive rare in females?
- Answer: Female needs two recessive alleles ( $X^h X^h$ ), requiring an affected father and at least a carrier mother.
Competency: 9:3:3:1 ratio.
- Answer: F2 Phenotypic ratio of a Dihybrid cross. 9 (both dominant), 3 (1st dom), 3 (2nd dom), 1 (both rec).
Case: Epigenetics.
- Answer: Environment affects gene expression without changing the DNA sequence.
Creating: "Mendel and Linkage".
- Answer: True. Linked genes do not separate, so he wouldn't have seen the independent combinations.
Designing: Mutation visual aid.
- Answer: Normal: BEAST. Deletion: BEST. Substitution: FEAST. Duplication: BEEAST.
Application: DNA Fingerprinting.
- Answer: Uses VNTRs (Variable Number Tandem Repeats) which are unique to individuals.
Critical Thinking: Blood group different from parents.
- Answer: Parents A ( $I^A i$ ) and B ( $I^B i$ ) can produce O ( $ii$ ) or AB ( $I^A I^B$ ).
Analysis: "Law of Purity of Gametes".
- Answer: Gametes receive only one allele for each trait during meiosis.

Section E: Advanced Competency

Scenario: Pure line of white (recessive).
- Answer: Just one generation. If the plant is white (tt), it is already pure.
Designing: Tongue Rolling study.
- Answer: Survey classmates, tally "Rollers" vs "Non-rollers", use Punnett square to estimate gene frequencies.
Application: Genetic Counseling.
- Answer: Advice for couples with family history of genetic disorders to understand risks.
Creating: Comic strip.
- Answer: [Description: Alleles T and t moving away during Anaphase I].
Case Study: Thalassemia (Carrier x Carrier).
- Answer: 25% risk of affected child (Major).
Multiple Alleles (ABO).
- Answer: Three alleles ( $I^A, I^B, i$ ) exist in the population for one gene.
Critical Thinking: Inbreeding risk.
- Answer: Increases the probability of harmful recessive alleles coming together in homozygous form.
Analysis: Y-linked vs X-linked.
- Answer: Y-linked (Holandric) passes from father to all sons. X-linked can skip generations via females.
Designing: Table of disorders.
- Answer: Haemophilia (X-linked rec, bleeding), Color-blindness (X-linked rec, vision), Thalassemia (Autosomal rec, anemia).
Creating: Mendel's conclusion.
- Answer: "Heredity is governed by discrete factors that segregate, assort independently, and follow rules of dominance."

Section A: Case-Based Questions

Case Study 1: Gregor Mendel crossed a tall pea plant with a dwarf pea plant. F1 were all tall. F2 had both tall and dwarf.

Identify the dominant and recessive traits.

Answer: Dominant: Tall (T). Recessive: Dwarf (t).

Why did the dwarf trait disappear in F1 and reappear in F2?

Answer: It was masked by the dominant 'T' allele in F1 (Tt). It reappeared in F2 when two recessive alleles came together (tt).

Designing: F2 Punnett square and ratios.

Answer: (T, t) x (T, t) -> TT, Tt, Tt, tt. Phenotypic Ratio: 3 Tall : 1 Dwarf. Genotypic Ratio: 1 TT : 2 Tt : 1 tt.

If Mendel chose Snapdragon (Incomplete dominance)?

Answer: F1 would have an intermediate phenotype (e.g., Pink if parents were Red and White).

Why choose the pea plant?

Answer: Short life cycle, many contrasting traits, easy to cross-pollinate, produces many offspring.

Case Study 2: Husband is color-blind, Wife has normal vision (father was color-blind). 6. Is color blindness autosomal or sex-linked?

Answer: Sex-linked (X-linked) recessive.

Genotype of the wife.

Answer: $X^C X^c$ (Carrier). Since her father was color-blind ( $X^c Y$ ), he must have passed the $X^c$ to her.

Creating: Pedigree chart.

Answer: [Description: Circle-Square connecting. Husband shaded, Wife half-shaded/dot].

Analysis: % chance son will be color-blind.

Answer: 50%. The son receives Y from father and either $X^C$ (Normal) or $X^c$ (Color-blind) from mother.

Why more common in males?

Answer: Males have only one X chromosome. A single recessive allele on the X chromosome is enough to cause the condition.

Section B: Assertion-Reasoning Questions

Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.

Assertion (A): A heterozygous individual expresses the dominant trait. Reason (R): The dominant allele masks the expression of the recessive allele.

Answer: (a) Both A and R are true and R is the correct explanation.

Assertion (A): The Law of Independent Assortment holds true for all pairs of characters. Reason (R): Linked genes do not assort independently.

Answer: (d) A is false but R is true. (Linked genes are an exception).

Assertion (A): Haemophilia is known as "Bleeder's disease". Reason (R): It is an X-linked recessive disorder where blood fails to clot.

Answer: (a) Both A and R are true and R is the correct explanation.

Assertion (A): Mutation is a sudden change in genes. Reason (R): Changes in gene structure can lead to variations.

Answer: (b) Both A and R are true but R doesn't explain the "sudden" nature.

Assertion (A): In humans, the father determines the sex of the child. Reason (R): The egg contains X, sperm can carry X or Y.

Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

Designing: Dihybrid cross RRYY x rryy.

Answer: Gametes: RY and ry. F1: RrYy (Round-Yellow).

Creating: Genetic Profile Bbtt.

Answer: Genotype: Bb (Heterozygous), tt (Homozygous recessive). Phenotype: Brown eyes (Dominant B), Straight hair (Recessive t).

Analysis: 25 short, 75 tall. Can you tell TT from Tt?

Answer: No. Both TT and Tt look identical (Tall) due to dominance.

Designing: Law of Segregation flowchart.

Answer: Parent (Tt) -> Meiosis -> Gamete 1 (T) and Gamete 2 (t) separate.

Visualisation: Locus and Alleles.

Answer: [Diagram: Two bars. Same spot marked A on one and a on the other].

Application: Blood Group AB.

Answer: Co-dominance. Both $I^A$ and $I^B$ alleles are expressed equally.

Creating: Two sparkling cats have a non-sparkling kitten.

Answer: Parents must be heterozygous (Ss). Cross: Ss x Ss -> 25% ss (non-sparkling).

Analysis: "Criss-cross inheritance".

Answer: Father passes the trait to daughter (carrier), who passes it to her son.

Designing: Pedigree checklist.

Answer: 1. Do unaffected parents have an affected child? (Recessive). 2. Does every affected child have an affected parent? (Dominant).

Creating: Dialogue.

Answer: Dominant: "I'm in charge here!" Recessive: "Fine, I'll wait until I meet someone just like me."

Section D: Competency & Critical Thinking

Genotype vs Genome.

Answer: Genotype: Genetic makeup of an individual for a specific trait. Genome: Total genetic material (all genes) of an organism.

Scenario: Test Cross.

Answer: Cross with 'tt'. If all offspring tall -> Parent is TT. If 50% tall, 50% dwarf -> Parent is Tt.

Critical Thinking: Two blue-eyed parents have a brown-eyed child?

Answer: Impossible if blue is recessive and brown is dominant.

Application: Sickle Cell Anemia.

Answer: Point mutation -> Valine instead of Glutamic acid -> Hb molecules clump -> RBCs become sickle-shaped.

Monogenic vs Polygenic.

Answer: Monogenic: Controlled by one gene (e.g., Pea height). Polygenic: Controlled by multiple genes (e.g., Human skin color).

Diagram Based: Punnett square fill-in.

Answer: (Standard 2x2 grid results).

Importance of Variation.

Answer: Helps species adapt to changing environments, reducing extinction risk.

Analysis: Why X-linked recessive rare in females?

Answer: Female needs two recessive alleles ( $X^h X^h$ ), requiring an affected father and at least a carrier mother.

Competency: 9:3:3:1 ratio.

Answer: F2 Phenotypic ratio of a Dihybrid cross. 9 (both dominant), 3 (1st dom), 3 (2nd dom), 1 (both rec).

Case: Epigenetics.

Answer: Environment affects gene expression without changing the DNA sequence.

Creating: "Mendel and Linkage".

Answer: True. Linked genes do not separate, so he wouldn't have seen the independent combinations.

Designing: Mutation visual aid.

Answer: Normal: BEAST. Deletion: BEST. Substitution: FEAST. Duplication: BEEAST.

Application: DNA Fingerprinting.

Answer: Uses VNTRs (Variable Number Tandem Repeats) which are unique to individuals.

Critical Thinking: Blood group different from parents.

Answer: Parents A ( $I^A i$ ) and B ( $I^B i$ ) can produce O ( $ii$ ) or AB ( $I^A I^B$ ).

Analysis: "Law of Purity of Gametes".

Answer: Gametes receive only one allele for each trait during meiosis.

Section E: Advanced Competency

Scenario: Pure line of white (recessive).

Answer: Just one generation. If the plant is white (tt), it is already pure.

Designing: Tongue Rolling study.

Answer: Survey classmates, tally "Rollers" vs "Non-rollers", use Punnett square to estimate gene frequencies.

Application: Genetic Counseling.

Answer: Advice for couples with family history of genetic disorders to understand risks.

Creating: Comic strip.

Answer: [Description: Alleles T and t moving away during Anaphase I].

Case Study: Thalassemia (Carrier x Carrier).

Answer: 25% risk of affected child (Major).

Multiple Alleles (ABO).

Answer: Three alleles ( $I^A, I^B, i$ ) exist in the population for one gene.

Critical Thinking: Inbreeding risk.

Answer: Increases the probability of harmful recessive alleles coming together in homozygous form.

Analysis: Y-linked vs X-linked.

Answer: Y-linked (Holandric) passes from father to all sons. X-linked can skip generations via females.

Designing: Table of disorders.

Answer: Haemophilia (X-linked rec, bleeding), Color-blindness (X-linked rec, vision), Thalassemia (Autosomal rec, anemia).

Creating: Mendel's conclusion.

Answer: "Heredity is governed by discrete factors that segregate, assort independently, and follow rules of dominance."

Genetics

Genetics - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page

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Genetics

Genetics - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Section B: Assertion-Reasoning Questions

Section C: Creating and Designing (Application & Analysis)

Section D: Competency & Critical Thinking

Section E: Advanced Competency

On this page